A constant concern exists as to the safety of vehicles where highways, streets and the like, intersect with railroad crossings. Despite the significant advances in technology utilized in both highway vehicles and trains, accidents involving collisions between trains and highway vehicles continue to occur, which accidents are generally catastrophic in nature.
Attempts to warn passenger vehicles and the like of oncoming trains involve many techniques that are old and well-known. For example, in U.S. Pat. No. 1,978,286 by Sommer, the system includes audio receiver equipment located on the train to detect the sound of whistles, warning bells and sounds to catch the general rumble of the train. Such sounds are coupled to the train-mounted receiver, which transmits the sounds by way of a radio transmitter. A receiver mounted in the vehicle then receives the transmission and alerts the vehicle occupants of the approaching train.
In U.S. Pat. No. 3,735,342 by Helliker et al, an alerting system is disclosed for alerting the occupant of a motor vehicle of the presence of an emergency vehicle siren. The frequencies generated by a typical siren are in the range of about 400-1500 Hertz. Three frequency-selective circuits in the receiver are responsive to sequentially detect the 600 Hz, 900 Hz and then 1200 Hz tones of the siren. On the detection of the specific sequence of frequencies, the motorist is alerted of the approaching emergency vehicle.
In U.S. Pat. No. 3,760,349 by Keister et al., an emergency warning system is disclosed in which a transmitter is mounted on an emergency vehicle for transmitting 500 Hz and 1000 Hz signals alternately modulated on an RF carrier. The transmitter is triggered when the siren is operated. A receiver in the motor vehicle receives the modulated signals, demodulates them and produces corresponding alternating audio signals to the vehicle operator, indicating the existence of a nearby emergency vehicle.
U.S. Pat. No. 4,942,395 by Ferrari et al., discloses a railroad grade crossing and motor vehicle warning system. In such system, a locomotive-mounted mounted transceiver transmits a coded radio signal to a transceiver mounted at the railroad crossing. The railroad crossing transceiver, in turn, transmits a shortwave radio signal to a vehicle-mounted receiver. The signal transmitted by the locomotive is apparently transmitted as long as the train is in motion.
U.S. Pat. No. 5,270,706 by Smith discloses a passive aircraft proximity detector for use with highway vehicles. According to this detector, a superheterodyne receiver mounted in the vehicle detects frequencies emitted from the aircraft, in the region of 900-1300 megahertz. On the detection of such frequencies, the receiver provides an indication to the vehicle when the aircraft is in range.
U.S. Pat. No. 5,235,329 by Jackson discloses an emergency vehicle detection device. Here, a signal in the citizens band frequency is transmitted by the emergency vehicle, in response to the actuation of a siren, and received by a receiver mounted in a near-by vehicle. The vehicle employs a band-selective receiver for detecting the particular frequency of transmission, or band of frequencies.
U.S. Pat. No. 5,278,553 by Cornett, et al. discloses a system of warning an approaching emergency vehicle. The system detects two frequencies that fall within the range of siren frequencies. When detection of such frequencies is sensed, audible and visible alarms are provided, and the vehicle sound system is de-energized.
Despite the disclosure of these warning systems, there is nevertheless a reluctance to adopt any one or more of the techniques on a widespread scale. By and large, the reason for this is that often both the emergency vehicle or train, as well as the highway vehicle to be warned, require modification or additional equipment, thereby involving an inconvenience during installation, as well as added expense. Indeed, and insofar as locomotives or rail traffic is concerned, any safety equipment for use thereon is governed by federal and other regulatory authorities. This necessarily incurs substantial expense in testing and approving the development of new equipment or any modification or addition to existing equipment. Further, in the event an alerting system is accepted on a widespread basis, such a system must be low-cost, reliable and easily implemented.
From the foregoing, it can be seen that a need exists for the provision of a detector for detecting the proximity of a train, without requiring any modification to the train at all, or at least only small modifications for enhanced performance. A further need exists for utilizing present train-transmitting facilities which are of high quality, which are reliable and time-tested type of equipment, where the transmissions thereof are received by remotely-located receivers. In this manner, on the routine transmission by a train, such as from the head end to the rear end thereof, or vice versa, such frequency can be detected by the remotely located receiver. A further need exists for a receiver utilizing conventionally available circuits, but provides a high degree of reliability and selectivity as to the transmissions by trains. Yet another need exists for utilizing frequencies allocated only to rail-type vehicles, thereby reducing the likelihood that other spurious frequencies will be received.